Isophorone nitrile (IPN) or 3-cyano-3,5,5-trimethylcyclohexanone is a critical intermediate in the synthetic scheme to the diisocyanate (IPDI). Numerous prior art processes have been developed to synthesize IPN. For example, Dubreux U.S. Pat. No. 4,299,775 discloses a two-phase process for the preparation of IPN by reacting isophorone (IPH) with a cyanide in the presence of a catalytic amount of a phase-transfer agent. The quaternary ammonium catalysts are used as their chloride or bromide-salts; the chloride or bromide ion is exchanged for cyanide ion and in this cyanide form is transferred from the water to the solvent layer via the well known phase transfer mechanism. German Patent No. 1,240,854 to Scholven-Chemie discloses a process for the preparation of IPN by reacting isophorone with hydrogen cyanide in the presence of a basic catalyst such as alkali cyanide, hydroxides or alcoholates. The catalyst is removed by washing with dilute nitric acid.
Japanese Laid-Open specification 61-33157 to Nippon Kagako K.K. discloses a process for the preparation of isophorone nitrile by reacting isophorone with hydrogen cyanide in the presence of tetra-n-butylammonium hydroxide, tetra-n-butylphosphonium hydroxide or benzyltrimethylammonium hydroxide. The resulting reaction liquid is washed in water.
Acidic washing to remove catalyst produces an aqueous effluent saturated in isophorone and containing some cyanide. Disposal of such an effluent adds significantly to the cost of the product.